A channel's message slots are named from the client, on every backend

The IR called them react-message and django-message, so a FastAPI channel had
to declare a DjangoMessage. They are client-message and server-message now,
and the direction words hold wherever a channel is declared: Params /
ClientMessage / ServerMessage, with mizan-core deriving <Pascal>Params and
friends so no backend names a type itself. Django's ReactChannel and
FastAPI's ReactChannel are both Channel.

mizan-fastapi never registered a channels extension, so build_ir() emitted no
channel at all and every payload type was invisible to codegen. It registers
one now. RegistryExtension is an ABC requiring all(), which is what the IR
reads — an extension that cannot enumerate its registrations no longer exists.

The gate that should have caught the rename could not: tests/afi registered no
channel because mizan-rust had no channel registry to register one in, so a
five-package rename of the wire contract passed byte-parity without a channel
byte crossing it. mizan-rust grows ChannelSlotKind, a CHANNELS slice, a
#[mizan::channel] macro, and KDL emission whose wire_to_pascal matches Python's
split; the AFI fixture now carries a channel with every slot and one with a
single slot, so all three backends prove the contract byte for byte.

MizanChannel held three Option<String> beside three has_*() predicates and
unwrapped them with defaults; it holds an ordered slot vector, so an absent
slot is absent rather than defaulted. The channels target emitted a React
hooks file that a stage1-only consumer could not compile — react emits that
now. The codegen's parity tests byte-compared emitted source against baselines
without ever compiling it: they compile the generated crate and run its tests,
import the generated Python package and call every method, and typecheck each
TypeScript target against a consumer.

Also fixed at source: app_visitor printed its import diagnostic to stdout, the
stream export_mizan_ir writes KDL to, so a failed import silently corrupted the
IR; the apps root was hardcoded to "apps"; _default_literal crashed build_ir on
any non-JSON-serializable field default; Django and mizan-core derived Pascal
names two different ways, disagreeing on every dotted channel name.

ir.py builds a document and renders templates/ir/document.kdl.j2 rather than
appending KDL strings with hand-tracked indentation, and named types resolve to
a fixed point — a model reachable only through a union branch was referenced by
a ref that no type block ever defined.

The rest is the write-gate's own classifiers run over the standing tree:
relative imports, silent swallows, Protocol contracts that should be ABCs,
emitters hand-rendering target source, catch-all arms over closed enums, and
comments narrating the project rather than the code.

Co-Authored-By: Claude Opus 5 (1M context) <noreply@anthropic.com>

backends/mizan-fastapi/tests/test_dispatch.py

@@ -88,7 +88,7 @@ def app():
 
     @client
     async def async_echo(request, text: str) -> EchoOutput:
-        # await something on the loop to prove we're really running async
+        # Yielding to the loop fails outright if the handler is not awaited.
         await asyncio.sleep(0)
         return EchoOutput(message=f"async: {text}")
 
@@ -183,18 +183,19 @@ class ContextFetchTests:
         assert r.json()["error"]["code"] == "NOT_FOUND"
 
 
-# ─── Invalidation ───────────────────────────────────────────────────────────
+# ─── Auth gating ────────────────────────────────────────────────────────────
 
 
 class AuthTests:
-    """The decorator normalizes auth=True → meta['auth']='required'; executor must match both."""
-
     def test_anonymous_request_to_auth_required_returns_401(self, http):
         r = http.post("/api/mizan/call/", json={"fn": "whoami", "args": {}})
         assert r.status_code == 401
         assert r.json()["error"]["code"] == "UNAUTHORIZED"
 
 
+# ─── Invalidation ───────────────────────────────────────────────────────────
+
+
 class InvalidationTests:
     def test_mutation_emits_invalidate_list(self, http):
         r = http.post(
@@ -211,8 +212,6 @@ class InvalidationTests:
 
 
 class StructuredOutputTests:
-    """list[BaseModel] and Optional[BaseModel] should reach the wire as bare values, not {result: ...}."""
-
     def test_list_of_basemodel_returns_bare_array(self, http):
         r = http.post("/api/mizan/call/", json={"fn": "list_items", "args": {}})
         assert r.status_code == 200
@@ -232,21 +231,20 @@ class StructuredOutputTests:
         assert r_missing.json()["result"] is None
 
 
-# ─── Merge protocol ─────────────────────────────────────────────────────────
+# ─── Async handlers ─────────────────────────────────────────────────────────
 
 
 class AsyncHandlerTests:
-    """`async def` handlers dispatch on the loop via view.acall."""
-
     def test_async_handler_returns_awaited_result(self, http):
         r = http.post("/api/mizan/call/", json={"fn": "async_echo", "args": {"text": "hello"}})
         assert r.status_code == 200
         assert r.json()["result"] == {"message": "async: hello"}
 
 
-class MergeTests:
-    """@client(merge=...) emits a `merge` field in the response so the kernel can splice without refetch."""
+# ─── Merge protocol ─────────────────────────────────────────────────────────
 
+
+class MergeTests:
     def test_merge_target_emits_merge_entry(self, http):
         r = http.post(
             "/api/mizan/call/",
@@ -254,9 +252,8 @@ class MergeTests:
         )
         assert r.status_code == 200
         body = r.json()
-        # Server resolves slot — items_list returns list[ItemOutput], mutation returns ItemOutput
+        # items_list returns list[ItemOutput], so the slot resolves to items_list.
         assert body["merge"] == [
             {"context": "items", "slot": "items_list", "value": {"id": 42, "name": "renamed"}}
         ]
-        # invalidate stays empty when only merge is declared
         assert body["invalidate"] == []